This invention relates to a fixture for holding a workpiece. More particularly, it involves a fixture for holding a semiconductor wafer during anodization.
Anodization is being increasingly employed in processing semiconductor devices. For example, selective anodization is often utilized to form multilevel aluminum conductors for an integrated circuit device. One method for anodizing semiconductor wafers is to attach a clip to the edge of the substrate and immerse most of the substrate in the anodizing solution. A positive potential is applied to the clip and a negative potential to the solution by means of a noble metal electrode in the solution. However, with this method the clipped edge of the substrate must remain out of the solution and consequently is not anodized. Also, both sides of the substrate will be anodized unless the back of the substrate is protected by an insulating coating. In another method, the substrate is placed on a vacuum chuck and immersed in the anodizing solution. A metal electrode in the chuck contacts the inward side of the wafer, with another electrode contacting the solution similar to that previously described. Unfortunately, however, the vacuum tends to draw the anodizing solution around or through any imperfections in the wafer-chuck seal thereby causing a conductive path which shorts the electrodes together thereby by-passing the substrate resulting in incomplete anodization.